Sewing apparatus and method

ABSTRACT

A tubular fabric article is gripped at either end on gripping rings ( 24 ) which can be rotated and moved axially with respect to a fixed position D-D. A fixed needle mechanism ( 30 ) extends within the tubular article. A needle ( 36 ) is oscillated between a retracted and extended position and cooperates with a hook and bobbin mechanism to form stitches.

This invention relates to a sewing apparatus, a sewing method, and a needle for use in the apparatus and method. The invention is particularly, but not exclusively, applicable to sewing reinforcement elements to tubular articles such as vascular grafts.

Vascular grafts are typically woven or knitted in tubular form from a synthetic fibre such as polyester and may be coated with resin or expanded PTFE. Diameters range from 8 mm to 42 mm. Reinforcing elements, typically of metal wire, are frequently attached to the exterior of the graft to aid shape retention, to act as a stent, or in the form of shape memory alloys to aid insertion via a catheter and subsequent deployment.

Currently, wire reinforcements are attached to vascular grafts by hand sewing. Since the wire diameter may be as little as 0.1 mm and the grafts themselves are small, this is a difficult and tedious operation which is costly, and it is difficult to ensure uniform quality.

It has been proposed to perform this operation with a modified sewing machine using a shuttle mechanism positioned within the graft on a long arm. However, this is impractical for small diameters of tubular graft. It would be necessary to use a very small shuttle which would carry a very limited amount of thread and require frequent reloading. Also, in the limited space within the graft it would be extremely difficult to form a needle thread loop sufficiently large to ensure consistent pick-up by the sewing hook.

U.S. Pat. No. 6,295,940 discloses an apparatus in which a vascular graft is loosely positioned on a cylindrical mandrel. The mandrel can be translated axially and the graft can be rotated on the mandrel by a feed roller. A lift finger in the mandrel is operable to lift a portion of the graft, the lifted portion then being held by a pinching device. A stitch is then made through the lifted portion adjacent the pinching device by a stitching means, which may be a sewing machine using a needle and a looper.

This apparatus has the disadvantage that the graft is subjected to pulling, stretching and pinching. Also, the relatively loose fit of the graft on the mandrel and the use of a feed roller make it difficult to achieve the required level of positional accuracy.

The present invention provides apparatus for sewing tubular articles, comprising:

-   -   holding means for holding the article at both ends;     -   a needle assembly positioned, in use, within the article, the         needle assembly comprising a needle having a needle point and an         eye adjacent to the needle point, and needle drive means for         cyclically driving the needle between a retracted position and         an extended position;     -   needle thread supply means for supplying a needle thread from a         reservoir to the eye of the needle;     -   a stitch-forming mechanism located in a position which is fixed         in relation to the needle assembly and which, in use, is outside         the tubular article, the stitch-forming mechanism being adapted         to form a stitch using a loop formed in the needle thread; and     -   motion means for producing relative axial and rotational motion         between the holding means and the needle assembly.

The invention also provides a needle for use in the foregoing apparatus, comprising a needle blade formed as an arc of a circle, a first end of the needle blade being formed as a needle point and the needle blade having an eye adjacent the needle point; and a second end of the needle blade being secured to or formed integrally with a needle shank, the needle shank being adapted to receive a pivotal mounting pin at a location within said circle.

From another aspect, the invention provides a method of sewing a tubular article comprising the steps of:

-   -   (a) passing a needle carrying a needle thread from the interior         of the article to the exterior;     -   (b) forming a loop in the needle thread exteriorly of the         article;     -   (c) using the needle thread loop to form a stitch;     -   (d) retracting the needle into the interior of the article;     -   (e) taking up the needle thread to close said loop;     -   (f) moving the article axially and/or rotationally with respect         to the needle location; and     -   (g) repeating steps (a) to (f).

Preferred features and advantages of the invention will be apparent from the claims and from the following description.

An embodiment of the invention will now be described, by way of example only, with reference to the drawings, in which:—

FIG. 1 is a plan view of one form of apparatus embodying the invention;

FIG. 2 shows part of FIG. 1 in greater detail;

FIG. 3 is an enlarged view of a needle and associated parts;

FIGS. 4A, 4B and 4C are a side view and views from either end of one form of needle;

FIGS. 5A, 5B and 5C are similar views of another form of needle;

FIG. 6 is a side view of a wire guide which may be used in the apparatus; and

FIG. 7 is a partial plan view illustrating the relationship between the wire guide and the needle position.

Referring to FIG. 1, the apparatus has a fixed frame including parallel rails 10. A carriage 12 mounted on the rails 10 can be driven in either direction by a servo or stepper motor 14 through a lead screw 16 and a precision ball mechanism (not shown) on the carriage 12.

Parallel arms 18 extend from the carriage. A drive shaft 20 is mounted for rotation in the arms 18 and is driven by a servo or stepper motor 22. A pair of fabric grip rings 24, axially aligned on axis A, are driven synchronously by the shaft 20 via toothed belts 26 and timing pulleys 28. A tubular article, such as a knitted vascular graft, can be clamped at either end to the grip rings 24 to extend along the axis A, and the motors 14 and 22 can be operated to position any selected point on the graft at a fixed location B. A stationary needle assembly (not shown in FIG. 1) extends through and between the arms 18. Referring to FIG. 2, the needle assembly is designated generally at 30 and comprises a hollow needle tube 32 extending from one side and secured to a rod 34 extending from the other side. Part of a needle 36 can be seen in FIG. 2 protruding from the needle tube 32.

Referring to FIG. 3, the needle tube 32 in this example is a stainless steel tube of 7 mm outside diameter. The needle 36, which will be described in greater detail below, comprises a needle blade 38 and a carrier or shank 40. The needle blade 38 is formed as a circular arc having an inner end secured to the shank 40 and an outer end formed with a point 42 and eye 44.

The shank is mounted on a pivot 46 and is driven through a pivoted link 48 by a drive rod 50. Thus, axial reciprocating motion of the drive rod 50 causes the needle 36 to oscillate in a circular path between the inner position shown in full in FIG. 3 and an outer position shown at 36 a. The centre of the pivot 46 is on the line D-D of FIG. 2. The needle tube 32 is slotted at 52 to allow passage of the needle blade 38 and to accommodate the top of the needle shank 40. A second slot is provided diametrically opposite at 54 in order to maximise the diameter of the needle 36.

It will be understood from the description thus far that the needle mechanism is placed inside the tubular article and that in making a stitch the needle point is passed through to the exterior of the article. The co-operating mechanism for forming the stitch is placed externally in a fixed position. When making vascular grafts it is necessary to use a lock stitch for reasons of safety and reliability, and therefore the co-operating mechanism is a conventional needle hook and bobbin arrangement. The location of the hook centreline is shown at C-C in FIG. 2. The hook and bobbin mechanism is well known per se and is not shown or described here.

It would be possible in principle to use a straight needle following a straight path from within the work piece. However, with the extremely small space available in the preferred applications of the invention, the length of such a needle would be very small and the loop formed by the needle thread would likewise be very small, too small to pass over any practicable shuttle or bobbin. The use of an arcuate needle maximises the length of the needle stroke, and thus the size of the needle thread loop, for a given size of needle tube. For the same reason, it is desirable to make the angular travel of the needle as great as possible, the arrangement shown in FIG. 3 providing about 135°, and to position the eye 44 as close as possible to the point 42.

FIG. 4 shows one form of needle in greater detail. The outer edge of the needle blade 38 is formed with a groove 56 extending from the rear of the needle blade at 58 to the eye 44. The purpose of the groove 56 is to guide the needle thread from its supply around the needle to the eye 44.

The needle shown in FIG. 5 is similar to that of FIG. 4 but with a different shape of shank.

In both FIGS. 4 and 5, the pivot arrangements are such that the angular movement of the needle would be limited to about 90°. The pivot arrangement of FIG. 3 is preferred for the reasons discussed above.

Having the needle inside the work in an “upside down” manner has advantages in addition to allowing very small tubes to be sewn. It allows better visibility of the sewing process, easier setting, and easier application of additional equipment to the fabric surface.

The needle is not only inverted, it is very small, tightly curved and mounted in an unconventional way. Also, the scarf is on the opposite side to that of conventional curved needles, thus allowing room for the sewing hook to approach the needle thread loop.

The needle should have as short a point as possible and the eye as near as possible to the point, to maximise the size of the needle thread loop. For sewing vascular grafts, because of the density of the fabric the needle requires a compromise between rigidity and a thin blade diameter, rigidity being paramount.

The examples of needle described above have a separate blade and shank. These may be made from straight needles by annealing, bending and re-hardening, and brazing or welding the resulting curved blade to the shank. However, the blade and shank could be made as an integral unit.

It will be understood that the needle thread is supplied through the needle tube from an external spool or reel, and that the needle thread is acted upon by a tension regulator and loop take-up device (typically a cam-operated arm) in the conventional manner but with these located outside the needle tube 32.

The apparatus of this embodiment is intended for use in sewing the metal wire components to vascular grafts. The components may be sets of discrete rings which can be supplied with spacers and clamped in position at the same time as the graft. Alternatively, a continuous wire may be applied in a helix or other predefined pattern. In this case the wire is conveniently run from a supply on a spool to a wire guide fixed close to the needle position.

FIG. 6 shows a wire guide comprising an arm 60 mounted on a base 62 by a spring at 64 and floating retainer at 66. The outer end of the arm 60 is formed with a wire guide 68 through which the wire is passed. As seen in FIG. 7, the arm 60 is shifted between positions at either side of the needle line 70 in synchronism with needle movement so as to hold the wire stationary as each stitch is made.

It will be understood that the stepper motors can be controlled, for example by a programmable logic controller, to shift the graft during retraction of the needle to produce a predetermined stitching pattern.

The arcuate needle described is preferred since it allows the needle mechanism to fit within a small tube. However, for larger diameter work it would be possible to use a straight needle operating radially.

The bobbin thread could be handled by another form of mechanism such as a boat shuttle. For workpieces less critical than vascular grafts, a chain stitch could be used instead of a lock stitch. 

1. Apparatus for sewing tubular articles, comprising: holding means for holding the article at both ends; a needle assembly positioned, in use, within the article, the needle assembly comprising a needle having a needle point and an eye adjacent to the needle point, the needle drive means for cyclically driving the needle between a retracted position and an extended position; needle thread supply means for supplying a needle thread from a reservoir to the eye of the needle; a stitch-forming mechanism located in a position which is fixed in relation to the needle assembly and which, in use, is outside the tubular article, the stitch-forming mechanism being adapted to form a stitch using a loop formed in the needle thread; and motion means for producing relative axial and rotational motion between the holding means and the needle assembly.
 2. Apparatus according to clam 1, in which the needle assembly and the stitch-forming mechanism are stationary in position and the holding means is moved axially and rotationally, with respect to them.
 3. Apparatus according to claim 2, in which the axial and rotational motion of the holding means is produced by means of servo motors or stepping motors.
 4. Apparatus according to claim 1, in which the stitch-forming mechanism comprises a hook and bobbin or a shuttle for passing a second thread through the needle thread loop to form a lock stitch.
 5. Apparatus according to claim 1, in which the needle assembly comprises a tubular support containing the needle and the needle drive means and through which is fed the needle thread.
 6. Apparatus according to claim 5, in which the needle is of arcuate form and is pivoted to the tubular support.
 7. Apparatus according to claim 6, in which the needle drive means comprises a push rod driving the needle through a pivoted link.
 8. Apparatus according to claim 7, in which the pivot points and the stroke of the push rod are so arranged that the needle oscillates through an angle greater than 90°.
 9. Apparatus according to claim 8, in which the needle oscillates through an angle of about
 1350. 10. A needle for use in the apparatus of claim 6, comprising a needle blade formed as an arc of a circle, a first end of the needle blade being formed as a needle point and the needle blade having an eye adjacent the needle point; and a second end of the needle blade being secured to or formed integrally with a needle shank, the needle shank being adapted to receive a pivotal mounting pin at a location within said circle.
 11. A needle according to claim 10, in which a thread groove is formed in the surface of the needle blade on the outside of the arc.
 12. A needle according to claim 11, in which said thread groove extends from the eye to said second end of the needle blade.
 13. (canceled)
 14. Apparatus according to claim 1, including a wire guide arranged to feed a reinforcement wire to the exterior of the tubular article adjacent the needle position.
 15. Apparatus according to claim 14, in which the wire guide is movable between two positions on either side of the needle position.
 16. A method of sewing a tubular article comprising the steps of: (a) passing a needle carrying a needle thread from the interior of the article to the exterior; (b) forming a loop in the needle thread exteriorly of the article; (c) using the needle thread loop to form a stitch; (d) retracting the needle into the interior of the article; (e) taking up the needle thread to close said loop; (f) moving the article axially and/or rotationally with respect to the needle location; and (g) repeating steps (a) to (f).
 17. The method of claim 16, in which the stitch is a lock stitch formed by passing a second thread through the loop of the needle thread. 